The present invention relates generally to roadmilling and trenching machine blocks and more particularly to a device and method for preventing wear on the face of roadmilling, trenching and other machine blocks that are used for retaining cutting bits.
Conventional roadmilling and trenching machines utilize cutting bits in normal operations. The cutting bits include a cutting surface located at an end of a cutting bit and a shank located at the other end of the cutting bit, and are rotated at rapid speeds. Means are provided to allow retention of the cutting bit shank within a bore of the machine block. In most instances, the cutting bit shank is retained within the bore by way of some form of retainer sleeve in combination with an enlarged end portion of the shank.
Due to rapid rotation of the cutting bit, excessive wear occurs on the face of the machine block into which the cutting bit shank extends. After prolonged use, the wear on the face of the machine block may become severe enough to require replacement of the machine block.
Several attempts have been made to alleviate the above noted problem. U.S. Pat. No. 4,561,698 (Beebe) refers to a sleeve and wear protector including an annular flange manufactured as a unitary wear protector. The unitary wear protector is manufactured of materials such that it wears at a rate substantially coincident with the wear rate of the cutting bit. However, Beebe is deficient in that the unitary construction of the wear protector requires replacement of the sleeve portion eventhough it may not be sufficiently worn to warrant replacement. Further, the unitary wear protector may rotate within the bore, thus leading to uneven wear of the protector assembly.
U.S. Pat. No. 4,489,986 (Dziak) refers to a retainer element mounted on a cylindrical shank of a cutter bit. The cutter bit is mounted within a bore of a block member. The shank fits within a retaining element which fits within a groove in the bore to prevent axial movement of the cutter bit. The block member includes a cylindrical portion upon which is mounted a wear collar. The cutter bit further has a shoulder which fits within the wear collar. Dziak fails to disclose a linkage between the wear collar, the retaining element and the block member.
It is, therefore, apparent that certain deficiencies exist in the conventional arrangement of roadmilling and trenching machines as regarding the retention of cutting bits therein.